Sonora expedition

The Sonora expedition was an American filibuster expedition to Mexico which occurred from 1853 to 1854. California lawyer William Walker led a small group of Americans into the Sonora region of Mexico to free the country from a corrupt dictatorship, but they were ultimately defeated by the Mexican Army and forced to flee back to the United States, where they were detained.

Background
In 1849, the southern American physician and adventurer William Walker arrived in San Francisco to work as a journalist during the Gold Rush. However, he fought in three duels and became a renegade, and he soon made plans to conquer vast regions of Latin America and create new slave states to join those already part of the USA. In the summer of 1853, he traveled to Guaymas (Baja California) in Mexico, seeking a grant from the government of Mexico to create a buffer frontier colony to protect against Native American raids. The Mexican government refused, but Walker came up with a more devious plan: he would take over the region anyway, and he hoped to create an independent "Republic of Sonora" which would later be admitted to the USA, just as the Republic of Texas had previously done.

War
On 15 October 1853, William Walker and 45 mercenaries set out from the port of San Francisco, California to occupy Guaymas. However, the Mexican Army had increased its troop strength and preparedness in the region after a French filibuster expedition had been repelled a year earlier. On 28 October, Walker's expedition arrived at Cabo San Lucas aboard the schooner Caroline, and they moved by sea to La Paz, the capital of Guaymas. After five days, they captured governor Rafael Espinosa, and filibusters hauled down the Mexican flag and replaced it with a flag with two stars, with the stars representing Sonora and Baja California. On 3 November 1853, the filibusters proclaimed the "Republic of Baja California", which would later evolve into the "Republic of Sonora" as Walker increased his territorial claims to the unconquered Sonora region. Walker made Henry P. Watkins his vice-president and implemented Louisiana's state constitution in the new country, legalizing slavery. The expedition of reinforcements from California - funded by American tycoons  - was slow in coming, however, and Walker decided to move his headquarters further north to Cabo San Lucas. Walker intended to wait for the USA to buy Sonora, but the civilian residents of La Paz clashed with the filibusters, and Walker portrayed his victory over the dissenters as a victory over the tyrannical and decadent Mexican government. He was later pressured to move the capital to the border town of Ensenada by the US Navy, and he requested American support in defending Baja California's independence. 253 Americans joined Walker after arriving on the boat Anita, but Walker would never be able to fully establish his control over the peninsula nor gain the support of the population. He faced resistance from the Mexican Army and civilians, among them Antonio Maria Melendrez's group, and many of Walker's troops mutinied. In the face of Melendrez' harassment and the desertion of another part of his troops, Walker and the remnants of his filibuster army surrendered to the US Army in San Diego on 8 May 1854, and Walker was acquitted of violating the Neutrality Act by a sympathetic jury.